Improper validation of certificate with host mismatch in cURL - CVE-2026-9547
Published: June 24, 2026
Vulnerability identifier: #VU135089
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-9547
CWE-ID: CWE-297
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: curl.haxx.se
Affected software:
cURL
cURL
Detailed vulnerability description
The vulnerability allows a remote attacker to perform a man-in-the-middle attack.
The vulnerability exists due to improper validation of certificate with host mismatch in the CURLOPT_SSH_KEYFUNCTION callback when validating SSH host keys for SCP:// or SFTP:// transfers. A remote attacker can present a host key type that does not match the key type already recorded for the host in the known_hosts file to perform a man-in-the-middle attack.
Only libcurl-based applications built with the libssh backend and using the callback are vulnerable. The curl command line tool is not affected.
How to mitigate CVE-2026-9547
Install security update from vendor's website.